Aiding GPS with calibrated Loran-C

GPS is currently being installed; when it is operational, five satellites will be in view virtually 100 percent of the time. However, the full constellation will not be in place for several years, and even then satellite failures may introduce coverage holes. Additionally, even with the full constellation, a GPS receiver will not always be able to monitor signal integrity unless some external aid is used. Loran-C can be used effectively to aid GPS. This paper reviews the theory of Loran propagation and gives a basic Loran pseudorange model. It also presents some basic approaches for combining Loran and GPS pseudoranges in a position-fixing receiver. Finally, it estimates the accuracy of the hybrid system.